I use RAW cells in DMEM + 10%FCS and "feed" them with heat treated (20 min 48C°) clatrin stained erythrocytes. I stimulate the RAW cells with 50ng/ml LPS and incubate the RAW cells and erys for about 12-15h. 

Under the light microscope I can't see that any RAWs engulfed any erys and when i FACS them i don't get any positives signals for claret.

I know that the erys are stained (just FACS the erys) and I know that my RAW can engulf things (silicon beads) 

How do I get my RAW to "eat" the erys?